Short-Circuit Evaluation in JavaScript: Boost Performance and Simplify Logic!

Have you ever wondered how ??, ||, and && work internally to determine the result they return? Is the result always correct? What’s the difference between them? No worries, buddy—let’s break it down and solve this peculiar mystery!🧐

Short-circuit evaluation in JavaScript refers to a programming concept where logical operators evaluate expressions from left to right and stop as soon as the result is determined.

Logical AND (&&):

It returns the first falsy value it encounters or the last value if all are truthy.

let x = 5;
let y = 0;

console.log(x && y);  // 0
console.log(x && true);  // true

Logical OR (||):

It returns the first truthy value it encounters or the last value if all are falsy.

let a = null;
let b = "Hello";

console.log(a || b);  // Hello
console.log(a || false);  //false

Nullish Coalescing Operator (??):

It’s used to provide a default value only when the left-hand operand is null or undefined.

let userName = null;
let result = 0 ?? 100;

console.log(result);  // 0
console.log(userName ?? "Guest")  // Guest

Combined Usage:

We can use them together as well, but it is recommended to use parentheses to avoid confusion and undesired results.

let a = null;
let b = 0;
let c = 10;
let d= 20

let result = (a ?? b) || (c && d);
console.log(result);  // 20

(a ?? b) → (null ?? 0) → 0 //since left is null
(c && d) → (10 && 20) → 20 //since left is truthy
(a ?? b) || (c && d) → ( 0 || 20) → 20 //since left is falsy

Merits:

• Optimizes performance by skipping unnecessary evaluations.
• Make the code cleaner and more readable.
• Prevent runtime errors by avoiding operations on null or undefined values.

Demerits:

• If a condition fails, it can be challenging to identify the issue during debugging.
• Can confuse readers about the intent.
• Can lead to unintended results

Best Practices:

• Use it for simple logic.
• Add comments to improve understanding of the logic for other coders.
• Use ?? instead of || when dealing with null or undefined values to avoid overriding falsy values like 0 or "".

Short-circuit evaluation is not limited to JavaScript; it is widely used in many programming languages such as Python, Java, C/C++, Kotlin, Go, Swift, and more. However, the symbols and usage can vary slightly depending on the language's syntax and conventions.

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